1. Field of the Invention
The present invention relates to an electronic component such as a piezoelectric resonator and, more specifically, to an improved surface mounting type electronic component in which an electronic component element is disposed between upper and lower case substrates.
2. Description of the Related Art
In a piezoelectric resonance device, such as a piezoelectric resonance element, a piezoelectric resonance element is packaged and sealed in such a way that oscillation thereof is not hindered in order to allow the piezoelectric resonance element to be surface-mounted on a printed circuit board or the like and to improve the environmental compatibility of the resonance element.
For example, Japanese Patent Laid-Open No. 4-70107 (Japanese Patent Application No. 2-183124) discloses a piezoelectric resonance device having a construction as shown in FIG. 11. In a piezoelectric resonance device 71, a piezoelectric resonance element 74 is formed by disposing resonance electrodes 73a and 73b on the major surfaces of a piezoelectric substrate 72 which has a rectangular plate shape. As shown in FIG. 12, in the piezoelectric resonance element 74, the resonance electrode 73a is provided at the center of one of the major surfaces of the piezoelectric substrate 72 and connected to a lead electrode 73d through a conductive connection portion 73c. Spaces 75a and 75b for allowing free and unhindered vibration are provided on the upper and lower sides of the piezoelectric resonance element 74. An upper case substrate 76a and a lower case substrate 76b which comprise rectangular plates having the same size as the piezoelectric substrate 72 are stacked together. External electrodes 77 and 78 are provided on an exterior of the piezoelectric resonance device 71.
Further, Japanese Utility Model Laid-Open No. 5-25818 (Japanese Utility Model Application No. 3-81444) discloses a piezoelectric resonance device as shown in FIG. 13. In this piezoelectric resonance device 81, a piezoelectric resonance element 83 is disposed in a case 82 having an upper opening. The upper opening of the case 82 is closed by joining a cover member 85 thereto via adhesive 84.
Further, Japanese Utility Model Laid-Open No. 4-69921 (Japanese Utility Model Application No. 2-113616) discloses a piezoelectric oscillation component as shown in FIG. 14. In this piezoelectric oscillation component 91, a case includes a case substrate 92 in the form of a rectangular plate and a rectangular-prism-shaped case member 93 having a lower opening and joined to the upper portion of the case substrate 92. A piezoelectric resonance element 94 is mounted on the case substrate 92.
Further, Japanese Utility Model Laid-Open No. 6-5215 (Japanese Utility Model Application No. 4-49012) discloses a chip-type piezoelectric oscillator 101 as shown in FIG. 15. In the chip-type piezoelectric oscillator 101, a piezoelectric element 102 in the form of a rectangular plate is sandwiched between case substrates 103 and 104 which are composed of rectangular plates. The side surfaces of the piezoelectric oscillator 101 are inclined in order to prevent external electrodes 105 and 106 from being separated when the piezoelectric oscillator 101 is mounted on a printed circuit board.
In the piezoelectric resonance device 71 shown in FIG. 11, the piezoelectric resonance element 74 and the upper and lower case substrates 76a and 76b have the same size. Thus, when assembling the device, the alignment of the piezoelectric resonance element 74 with the upper and lower case substrates 76a and 76b is rather difficult to perform. When the piezoelectric resonance element 74 and the upper and lower case substrates 76a and 76b are assembled such that there is a deviation in alignment between any of the element 74 and substrates 76a, 76b, cracks, chips, and other problems are generated in the piezoelectric resonance element 74 when it is handled.
In the piezoelectric resonance device 81 shown in FIG. 13, the piezoelectric resonance element 83 is disposed in a case, so that cracks, chips, and other problems are not easily generated in the piezoelectric resonance element as in the above described case. However, since the piezoelectric resonance element 83 is disposed in a case which is larger than the resonance element 83, it is extremely difficult to meet the demand for a reduction in size of the component.
Similarly, in the piezoelectric resonance device 91 shown in FIG. 14 also, it is rather difficult to meet the demand for a reduction in size due to the construction in which the piezoelectric resonance element 94 is arranged in the case formed by the lower case substrate 92 and the case member 93.
The piezoelectric oscillator 101 shown in FIG. 15 has the same problem as the piezoelectric resonance device shown in FIG. 12 although the sizes of the piezoelectric element 102 and the upper and lower cases 103 and 104 are different. That is, in the piezoelectric oscillator 101, the joining areas are the same in the joint section where the piezoelectric element 102 is joined to the lower case substrate 103. Further, in the joint section where the piezoelectric element 102 is joined to the upper case substrate 104, the areas of the portions corresponding to the joint interface are the same. Thus, the alignment of these portions is extremely difficult to perform. When the alignment is not performed in a satisfactory manner, cracks, chips, and other problems are liable to be generated in the piezoelectric element 102 when the oscillator is handled.
The above problems are experienced not only in surface mounting type electronic components using piezoelectric elements but also in surface mounting type electronic components using other electronic component elements.